Re: lost interface ID on Linux machine

Hi,

By "ID number", I assume that you mean the ifIndex?

The ifIndex is not guaranteed to be persistent over reboots, and this
is a quite common occurence. The relevant RFC text is below:

"Its value ranges between 1 and the value of ifNumber.  The
        value for each interface must remain constant at least from
        one re-initialization of the entity's network management
        system to the next re-initialization."

In other words, the ifIndex numbering of the interfaces is only
guaranteed to persist until the machine is re-booted.
But surely, if you want to know which interface is which, you can just
inspect the ifDescr field instead?

As an aside, some systems seem to be able to have ifIndex persistence
enabled, like some Cisco equipment:
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080134eec.shtml

Regards,
Joel Hansell

On Mon, Apr 23, 2012 at 4:47 AM, Usuário do Sistema <[email protected]> wrote:
> Hello, I have a CentOS 5.4 Linux machine and I'm monitoring by snmp it
> interfaces ethernet. but, when the machine it is restart ID number
> snmp that's interfaces are change.
>
> for exemplo when the linux machine is with ID 3 on interface eth1 and
> it is reset so it come up with a different ID for exemplo 2 for eth1.
>
> so I wonder why happen ? it's normal ? it's possible set a ID value
> for every interface ?
>
> if is change the ID number for each interface so stop my monitoring
> because my snmp software read by interface ID.
>
>
> thanks
>
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